The invention is related to the technical field of braking devices for all types of vehicles, particularly motor cars, motorbikes, etc.
Essentially, a braking device, regardless of its type, comprises a master cylinder connected hydraulically to calipers mounted at the members that brake the wheels of the vehicle, particularly disks carried by the hubs. The calipers accommodate pistons to act, under a pressure force resulting from force exerted on an actuating member that can be operated by hand or using the foot depending on the type of vehicle considered, on pads collaborating with the disks.
The purpose of the braking action is to decelerate the vehicle, possibly then bringing the latter to a complete standstill. The effect of this braking action is to cause mass to be transferred forward, thus altering the attitude of the vehicle which has a tendency to dive down at the front, consequently unloading the rear axial assembly in the case of a car, or the rear wheel in the case of a motorbike. Obviously, the risk of toppling toward the front of the vehicle during a braking action is far more serious and occurs far more frequently in the case of a two-wheeled vehicle, such as motorbikes for example.
Reference is made to FIG. 1 which shows and explains this toppling-forward phenomenon in the case of a motorbike. In this figure, xcex1 is the angle formed by the horizontal and the straight line connecting the point of contact of the front wheel and the center of gravity of the rider and of the bike. If P is the acceleration due to gravity directed vertically downward and D is the deceleration due to braking then the limit of toppling toward the front of the vehicle is reached when the deceleration is greater than or equal to the ratio of the acceleration P to the tangent of the angle xcex1. The limit of deceleration is determined by the adhesion of the tire to the road. Let this limit be known as xcexc. By way of entirely nonlimiting indication, a maximum xcexc value of 1.5 is commonly found in the dry and a xcexc value of 1 in the wet. For example, in the case of a sports bike, of the type illustrated in FIG. 1, the angle xcex1 is close to 45xc2x0, it being possible for the bike to topple forward, if the maximum limit of adhesion is greater than 1 on horizontal ground. If the bike is traveling downhill, the toppling may occur for a xcexc value greater than 0.9.
The result therefore is that the risk of toppling forward under braking is particularly present, except in the case of unsure adhesion, and this represents a significant danger. Indeed, with the rear wheel no longer touching the ground, the vehicle will not longer be guided or controllable. In addition, particularly in the case of a motorbike, in which the position is unstable, if the rider does not have the reflex action of instantly releasing the brakes, the machine will flip over completely.
It is also found that the various systems proposed for preventing the wheels, particularly the front wheels, from locking in the event of excessive braking, remain inoperative once the xcexc value exceeds 0.8 to 1, for the reason that braking will result in the vehicle toppling forward, inevitably leading to an accident. More generally, any vehicle for which the tangent of the angle xcex1 is greater than 1/xcexc exhibits risks of toppling under braking.
The prior art can be illustrated by the teachings of patent EP 0 524 821 which discloses a brake control system comprising means for determining that a load of adhesion to the ground of the rear wheel is lower than or equal to a predetermined value of the deceleration. The system comprises control means for reducing and controlling a braking force at the brake of the front wheel on the basis of the previously determined results. Such control means are intended to prevent the front wheel from locking.
Patent EP 0 537 724 relates to a method for regulating the braking force of motorbikes, its objective being to be able to detect a detachment signal signifying adhesion of the rear wheel to the ground. The implementation means essentially consist of speed sensors, rotation sensors, microprocessors, pressure modulators, switching flaps, etc. This is therefore an entirely electronic system which does not make it possible to avoid detachment of the rear wheel but which, on the contrary, detects detachment of the rear wheel in order to act on the braking system and reduce the pressure at the front brake in order to allow the rear wheel to make contact with the ground again.
Such a system therefore does not make it possible to avoid the rear wheel lifting but, at the very most, makes it possible to avoid the bike toppling forward, all this being purely theoretical because it is quite clear that the rider will have the utmost difficulty controlling the bike when the rear wheel is off the ground.
The invention has set itself the object of solving these drawbacks in a simple, reliable, effective and rational way.
The problem that the invention sets out to solve is that of avoiding any detachment of the rear wheel or wheels of any type of vehicle in the event of heavy braking when there is significant deceleration causing mass to be transferred forward and therefore causing the rear axle assembly or the rear wheel to be unloaded in a way likely to cause toppling toward the front of the vehicle. As mentioned, this issue is more sensitive in the case of a two-wheeled vehicle of the motorbike type.
To solve said problem of measuring the load exerted on the rear wheel or wheels in order to determine the limit of adhesion of this or these rear wheel or wheels beyond which the toppling-forward phenomenon may arise, there has been designed and developed a braking device which comprises means which are connected to the hydraulic braking circuit and connected to at least one damping element of the rear wheel or wheels, said means being able to measure the load exerted on the rear wheel or wheels in conjunction with means able to decrease the pressure at the calipers of the front wheel or wheels and able to supply the necessary load to the rear wheel or wheels of the vehicle to prevent any unwanted lifting of said rear wheel or wheels in the event of heavy braking.
Advantageously, the means able to measure the load exerted on the rear wheel or wheels consist of a piston mounted coaxially with respect to the damping element and able to be displaced linearly, in a limited manner, with the ability for sealed guidance in a recess of a distribution support block secured to a fixed part of the vehicle, said recess being in communication with the hydraulic braking circuit at the master cylinder and the caliper of the front wheel or wheels.
To solve said problem of limiting the braking of the front wheel or wheels of the vehicle, so as to maintain a determined load on the rear wheel or wheels, the means able to reduce the pressure consist of a valve mounted coaxially at the end of the piston in conjunction with arrangements to be controlled under the effect of the displacement of said piston with a view to regulating the hydraulic pressure particularly at the caliper of the front wheel or wheels.
Advantageously, the valve comprises a body secured to a bore formed at the end of the piston, said body having an internal recess acting as a seat for a ball subject to an elastic member, said recess being in communication with the hydraulic circuit of the master cylinder, the ball being able to collaborate with a fixed element under the effect of the displacement of the piston to move it away from its seat.
To solve said problem of connecting the deceleration to a determined load considered as normal, exerted on the rear wheel or wheels, the piston of the valve is in abutment against a fixed part of the support block, the ball being away from its seat to allow fluid from the master cylinder to pass toward the caliper of the front wheel or wheels; conversely, when said load is not considered to be sufficient, there is a relative displacement of the piston of the valve and of the block as far as another extreme position of abutment corresponding to the ball being positioned in the bottom of its seat to reduce the pressure sent to said caliper.
The fixed element collaborating with the ball consists of a screw secured to the support block and opening into the recesses and of said block and of the body of the valve.
Another problem that the invention sets out to solve is that of being able to determine the minimum load that needs to be guaranteed on the rear wheel or wheels. To this end, the support block in which the piston of the valve is mounted with the capability for linear displacement is coupled to the damping element in conjunction with means of adjusting the load exerted on the rear wheel or wheels.
Another problem that the invention sets out to solve is that of being able, if necessary, to slow the displacement of the piston. To this end, the piston of the valve is mounted inside the block with the capacity for linear displacement against a hydraulic damping means.